Formation of plasma around a small meteoroid: 2. Implications for radar head echo

摘要

This paper calculates the spatial distribution of the plasma responsible for radar head echoes by applying the kinetic theory developed in the companion paper. This results in a set of analytic expressions for the plasma density as a function of distance from the meteoroid. It shows that at distances less than a collisional mean free path from the meteoroid surface, the plasma density drops in proportion to 1∕R where R is the distance from the meteoroid center; and, at distances much longer than the mean-free-path behind the meteoroid, the density diminishes at a rate proportional to 1∕R2. The results of this paper should be used for modeling and analysis of radar head echoes. Plain Language Summary Every second millions of submilligram meteoroids enter the Earth's atmosphere where they disintegrate, leaving behind atoms of iron, sulphur, carbon, oxygen, etc. Most of these small meteoroids cannot be seen by naked eye. However, when entering the atmosphere with the hypersonic speed of tens of kilometers per second, these meteoroids collide with atmosphere, heat up, and lose their material in a process called ablation. The ablated atoms and molecules further collide with atmospheric constituents, scatter, and ionize, producing dense plasmas around the meteoroid. Radars easily detect these plasmas, and researchers use these data to characterize both the meteoroids and the atmosphere. This paper produces analytic expressions describing the spatial distribution of plasma the small ablating meteoroid. This distribution can be employed for computer modeling of one kind of radar signals: head echo.